make fastopen fall back to connect if len==0

io.h

@@ -177,7 +177,7 @@ enum {
   IOM_WRITE=2,
   IOM_ERROR=4
 };
-/* return -1 if error, or | of IOM_READ, IOM_WRITE or IOM_ERROR */
+/* return -1 if error, events can be IOM_READ or IOM_WRITE */
 int iom_add(iomux_t* c,int64 s,unsigned int events);
 
 /* Blocking wait for single event, timeout in milliseconds */

socket/socket_fastopen_connect4.c

@@ -13,7 +13,11 @@ ssize_t socket_fastopen_connect4(int s,const char* ip,uint16 port,const char* bu
   int r;
   {
 #else
-  int r=socket_send4_flag(s,buf,len,ip,port,MSG_FASTOPEN);
+  int r;
+  if (len)
+    r=socket_send4_flag(s,buf,len,ip,port,MSG_FASTOPEN);
+  else
+    r=socket_connect4(s,ip,port);
   if (r==-1 && errno==ENOTCONN) {
 #endif
     /* apparently the kernel does not support TCP fast open */

socket/socket_fastopen_connect6.c

@@ -13,7 +13,11 @@ ssize_t socket_fastopen_connect6(int s,const char* ip,uint16 port,uint32_t scope
   int r;
   {
 #else
-  int r=socket_send6_flag(s,buf,len,ip,port,scope_id,MSG_FASTOPEN);
+  int r;
+  if (len)
+    r=socket_send6_flag(s,buf,len,ip,port,scope_id,MSG_FASTOPEN);
+  else
+    r=socket_connect6(s,ip,port,scope_id);
   if (r==-1 && errno==ENOTCONN) {
 #endif
     /* apparently the kernel does not support TCP fast open */